<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>promise的all方法</title>
</head>
<body>

</body>
<script>
// promise.all() 将多个promise实例合并成一个新实例
// 只有所有的promise实例的状态都为fulfilled，最终结果才能执行.then
// 如果有一个promise实例的状态为rejected，那么最终结果会执行.catch
let promise1 = new Promise((resolve, reject) => {
    setTimeout(() => {
        resolve(1000)
    }, 1000)
})
let promise2 = new Promise((resolve, reject) => {
    setTimeout(() => {
        resolve('hello')
    }, 1000)
})
let promise3 = new Promise((resolve, reject) => {
    setTimeout(() => {
        reject('promise3失败了')
    }, 1000)
})
let promise4 = Promise.all([promise1, promise2, promise3])
.then((res) => {
    console.log(res);
})
.catch((err) => {
    console.log(err)
})
</script>
</html>